The present application relates to the field of radiographic imaging. It finds particular application with the provision of radiation detectors in a radiography imaging system (e.g., mammography system, general radiology system, etc).
Radiographic imaging systems, such as projection radiography, computed tomography (CT) systems, line scanners, etc., provide information, or images, of the inside of an object under examination (e.g., interior aspects of an object under examination). Generally, the object is exposed to radiation, and one or more images are formed based upon the radiation absorbed by the object, or rather an amount of radiation that is able to pass through the object. Typically, highly dense objects absorb (e.g., attenuate) more radiation than less dense objects, and thus an object having a higher density, such as a bone or gun, for example, will appear differently than less dense objects, such as fatty tissue or clothing, for example. A detector array, generally positioned opposite a radiation source from which radiation is emitted relative the object under examination, is configured to detect radiation that traverses the object under examination and convert such radiation into signals and/or data that may be processed to produce the image(s). Such an image(s) may be viewed by security personnel to detect threat items (e.g., weapons, explosives, etc.) and/or viewed by medical personnel to detect medical condition.
In some scanners, such as projection radiography and three-dimensional imaging scanners (e.g., CT scanners), for example, the detector array and radiation source are mounted on opposing sides of a radiographic system, with the object under examination disposed there-between. In such a scanner, the radiation source emits a desired fluence of radiation directed toward the object under examination. The radiation is attenuated as it passes through the object under examination and reaches the detector on the other side. Digital image data of the object under examination can be produced by converting the detected radiation into an electrical signal (e.g., current or voltage) and measuring it. The number of photons that impact the detector is proportional to the amount of electrical signal measured by the detector. After that, an analog electrical signal from the detector is converted to a digital signal, and the digital signal can be used to create the image.
Flat panel detectors are typically used for projection radiography, where a burst of x-rays are directed toward an object and the flat panel detector is positioned behind the object. Projection radiography is typically utilized to produce two-dimensional images of an object (e.g., to diagnose internal medical issues in a patient, to examine internal objects in a suitcase). A flat panel detector can create digital image data, which can be used to produce images on a computer monitor or some other form of electronic display (or print-out).
Flat panel detectors (FPDs) can convert radiation to electrical signal(s), either directly or indirectly. An indirect FPD uses scintillators, for example, that convert x-ray photons to visible light photons, and has photodiodes distributed in a 2D array that detect the visible light photons and covert them to an electrical charge, which can then be converted to a digital signal. Alternately, direct FPDs utilize a radiation detection material that can convert x-ray photons directly into an electrical charge. For example, an amorphous selenium layer can create an electrical charge proportional to a number of impinging x-ray photons, and a 2D capacitor array can collect the electrical charges. In this both cases, the detector array can be addressed or mapped to respective pixels of the image.
Blocking layers are often implemented in a direct conversion FPD to allow (substantially) only one type of electrical charge (positive or negative) to transition or pass through one or more layers in the FPD while (substantially) blocking the transit of the opposite type of electrical charge. For example, blocking layers can be disposed at either side of a radiation detection layer to “block in” one type of charge within the radiation detection layer while allowing the opposite type of charge to “exit” the radiation detection layer. However, blocking layers, separation layers, and insulating layers are typically challenging to deposit. Furthermore, blocking layers are difficult to implement when they have to interface with chemically incompatible materials and/or there are contradictory requirements between their thickness and/or dielectric properties, for example.